Looking for recommendations for a small case that would take an ATX motherboard. Without going to some of the pricey large Silverstone HTPC cases or a mountainmods "HTPC" case is the Antec 300 about the most compact?

Check out the fractal design arc midi or mini.. I'm almost looking to pull the trigger on the midi. I like it because you can house a h100 without any mods. Some say the Bitfenix Shinobi is a good case.

If its not a system that requires tons of cooling then Id suggest looking at some of the Lian-Li cases that have a front-mounted PSU. The whole case is at tall as a standard ATX board, so much shorter and smaller than normal - worth a look i'd say!